They sell autoglym worldwide.
I think Amazon can be a good place to buy it but most auto shops stock it too.
Autoglym have a supplier-locator function on their website.

Dawn is great at cutting through any residue grease or oil, but as you say, it then negatively affects the hair condition.
Someone suggested filling a basin with warm water, then adding a bit of Dawn and swishing the hair around in that as a less harsh method.
Previously I'd been pouring it straight on to the base.

I've recently changed to trying 2 new things.
1) after using Dawn (or here in the UK its called Fairy Liquid !) I pat dry the system and then use a spray leave in conditioner/detangler (Johnsons No More Tangles) and that helped with the hair condition or
2) I ditched the Dawn and started using Tresemme Clarifying Shampoo.
This seems to cut through and remove any grease but is gentler on the hair.

I still use the Johnsons leave-in conditioner every day though.